Investigating the sensitivity of numerical model simulations of the modern state of the Greenland ice-sheet and its future response to climate change E. J. Stone1, D. J. Lunt1, I. C. Rutt2, and E. Hanna31BRIDGE, School of Geographical Sciences, University of Bristol, Bristol, UK2School of the Environment and Society, Swansea University, Swansea, UK3Department of Geography, University of Sheffield, Sheffield, UK

Abstract. Ice thickness and bedrock topography are essential boundary conditions for
numerical modelling of the evolution of the Greenland ice-sheet (GrIS). The
datasets currently in use by the majority of GrIS modelling studies are over
two decades old and based on data collected from the 1970s and 80s. We use a
newer, high-resolution Digital Elevation Model of the GrIS and new
temperature and precipitation forcings to drive the Glimmer ice-sheet model
offline under steady state, present day climatic conditions. Comparisons are
made of ice-sheet geometry between these new datasets and older ones used in
the EISMINT-3 exercise. We find that changing to the newer bedrock and ice
thickness makes the greatest difference to Greenland ice volume and ice
surface extent. When all boundary conditions and forcings are simultaneously
changed to the newer datasets the ice-sheet is 33% larger in volume
compared with observation and 17% larger than that modelled by EISMINT-3.

We performed a tuning exercise to improve the modelled present day
ice-sheet. Several solutions were chosen in order to represent improvement
in different aspects of the GrIS geometry: ice thickness, ice volume and ice
surface extent. We applied these new parameter sets for Glimmer to several
future climate scenarios where atmospheric CO2 concentration was
elevated to 400, 560 and 1120 ppmv (compared with 280 ppmv in the control)
using a fully coupled General Circulation Model. Collapse of the ice-sheet
was found to occur between 400 and 560 ppmv, a threshold substantially lower
than previously modelled using the standard EISMINT-3 setup. This work
highlights the need to assess carefully boundary conditions and forcings
required by ice-sheet models, particularly in terms of the abstractions
required for large-scale ice-sheet models, and the implications that these
can have on predictions of ice-sheet geometry under past and future climate
scenarios.

Citation: Stone, E. J., Lunt, D. J., Rutt, I. C., and Hanna, E.: Investigating the sensitivity of numerical model simulations of the modern state of the Greenland ice-sheet and its future response to climate change, The Cryosphere, 4, 397-417, doi:10.5194/tc-4-397-2010, 2010.